Wobble signal reproducing circuit

ABSTRACT

The present invention has an object to stably reproduce wobble signals of all disks of CD-R/RW, DVD-R/RW and DVD-RAM by one wobble signal reproducing circuit. In the wobble signal reproducing circuit, an AGC (AUTOMATIC GAIN CONTROL) circuit for equating a push-pull circuit output of a wide range and an RF amplitude of an optical detector output of two systems obtained by push-pull, and an AGC (AUTOMATIC GAIN CONTROL) circuit for making a wobble amplitude uniform are provided with a function to hold a gain or to change over a response time constant, and at the time of reproduction of the DVD-R/RW, a land pre-pit region is detected by the push-pull output to hold AGC (AUTOMATIC GAIN CONTROL) or change over a response time constant. Besides, in an address information recording region (PID region) at the time of reproduction of the DVD-RAM, the AGC (AUTOMATIC GAIN CONTROL) is held or the response time constant is changed over.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reproducing circuit of a wobblesignal recorded on a recordable disk of an optical disk.

2. Description of the Related Art

At present, a write once optical disk such as a CD-R/DVD-R, and arecordable optical disk such as a CD-RW/DVD-RW or DVD-RAM, in additionto a read-only optical disk such as a CD or a DVD-RAM, are put on themarket. At the time of recording of these recordable optical disks,clock signal generation from a reproduction signal, which is performedin a conventional read-only disk, can not be performed. Thus, a grooveas a portion where information is recorded on a disk is wobbled at aconstant period, and a clock signal at the time of recording isgenerated from a wobble signal obtained by reproducing this wobbling(hereinafter referred to as wobble) by a push-pull system.

FIG. 2 shows a conventional example of a wobble signal reproducingcircuit. Reflected light from a laser spot irradiated on a disk forms afar field pattern 2 on an optical detector 1 divided in two. Two outputsof the optical detector are subtracted by a subtracting circuit 17 totake out a push-pull component. From the obtained push-pull signal, awobble frequency is extracted by a band pass filter (BPF) 18. A wobblesignal reproduced from a CD-R/RW is a continuous signal of a frequencyof 22.05 KHz±1 KHz. In the CD-R/RW, since address information calledATIP (Absolute Time In Pregroove) is superimposed on the wobble signalby FM modulation, it has a width in frequency band. FIG. 3 is a viewshowing a disk surface of a DVD-R/RW. Reference numeral 301 in thedrawing designates a groove in which data is recorded and which iswobbled similarly to the CD-R/RW. A wobble signal reproduced in theDVD-R/RW is a continuous signal of a single frequency of 140.65 KHzdifferent from the CD-R/RW, and address information is not superimposed.Instead thereof, a pit called a land pre-pit (hereinafter referred to asan LPP) designated by 302 is recorded in a land portion which is betweena groove and a groove and in which information is not recorded. The LPPexists in a region from the head of maximum amplitude position of awobble to the third, and address information is recorded by this threebits.

In order to stably extract the wobble signal from the push-pull signal,it becomes necessary to reduce leakage of an RF signal to the push-pullsignal. Thus, as disclosed in Japanese Patent Unexamined Publication No.Hei. 8-194969, it is conceivable that an automatic gain control circuit(AGC circuit) is provided at a front stage of the subtracting circuit ofFIG. 2.

Besides, in recent years, as the capacity of a disk is increased,doubling of the speed of disk reproduction becomes active.

In double speed reproduction, it becomes necessary to change over thepass band of the BPF of wobble in connection with the double speed. As amethod of causing this connection, although it is conceivable thatsetting of the pass band of the BPF is changed over by a microcomputeraccording to the reproducing speed of a disk, since access to themicrocomputer becomes necessary each time the speed is changed, theprocessing becomes troublesome. In the case where CAV reproduction isperformed with an increase in speed of disk reproduction, a deviation inband setting of the BPF occurs by the restriction on the number ofaccesses to the microcomputer, and this becomes a factor of a drop inS/N of the wobble signal and an increase in clock jitter due to that.With respect to this problem, as disclosed in Japanese Patent UnexaminedPublication No. Hei. 11-203681, it is conceivable to use pass bandautomatic tracking by a dummy filter and a phase comparison circuit.

SUMMARY OF THE INVENTION

As set forth above, in the case where double speed reproduction ofvarious disks is realized by one optical disk reproducing device, sincethe specifications of the respective disks are different, variousproblems occur. The problems of a wobble signal reproducing circuit areas follows:

1. Leakage of a Land Pre-Pit Signal of a DVD-R/RW into a Wobble Signal

Here, in the case where the AGC (AUTOMATIC GAIN CONTROL) circuit isdisposed at the front stage of the subtracting circuit of FIG. 2 asdisclosed in Japanese Patent Unexamined Publication No. Hei. 8-194969,at the time of reproduction of a DVD-R/RW, an LPP signal leaks into anRF signal, and an AGC (AUTOMATIC GAIN CONTROL) gain is varied inaccordance with the amplitude variation. Thus, there is a fear that theRF signal at the time of passing through the LPP leaks into the wobblesignal.

2. The Processing for Lack of a Wobble Signal in an Address InformationRegion of a DVD-RAM

FIG. 4 is a view showing a disk surface of a DVD-RAM. Reference numeral403 in the drawing designates a groove; and 404, a land. In order toraise recording density, the DVD-RAM adopts a land groove recordingsystem in which signals are recorded in both the groove 403 and the land404. Thus, address information in the DVD-RAM is recorded in astaggering manner with respect to respective tracks of the land and thegroove as indicated by 401 and 402 of the drawing. The portion where theaddress information is recorded is called a PID (Physical IdentificationData) region.

Although a wobble signal reproduced in the DVD-RAM has a singlefrequency of 157 KHz similarly to the DVD-R/RW, since the addressinformation is recorded in the staggering manner in the PID region, whena push-pull component is detected and is subtracted, it lacks a signalat one side before the subtraction. Thus, similarly to the above item 1,in the case of considering provision of the AGC (AUTOMATIC GAIN CONTROL)circuit at the front stage of the subtracting circuit, it is conceivablethat the AGC (AUTOMATIC GAIN CONTROL) is saturated in the PID region.

Besides, the wobble signal reproduced in a CD-R/RW has a band width, andthe amplitude is varied. In order to reduce an offset due to that atbinarization at a later stage, as disclosed in Japanese PatentUnexamined Publication No. Hei 11-161961, it is conceivable that an AGC(AUTOMATIC GAIN CONTROL) circuit is provided at a later stage of the BPF18. However, in the DVD-RAM, since the groove does not exist in the PIDregion, it lacks the wobble signal at the time of reproduction of thePID region. Thus, similarly to the above, it is conceivable that thisAGC (AUTOMATIC GAIN CONTROL) circuit is saturated in the PID region.

3. BPF Pass Band Setting

In the technique disclosed in Japanese Patent Unexamined Publication No.Hei 11-203681, there are a problem of accuracy of wobble signal banddetection in the dummy filter and the phase comparison circuit, and aproblem that a circuit scale is increased in order to improve theaccuracy of the circuit. In the case where band setting of the BPF ismade to follow a clock signal reproduced from a wobble signal, itbecomes a problem that a ratio of a wobble signal frequency to a clockfrequency is different according to the kind of a disk.

Like this, since the specifications of the wobble signals are differentaccording to the disks, there has been a problem that in the case wherethe wobble signal reproducing circuits corresponding to the respectivedisks are provided, a circuit mounting area is increased.

In order to solve the above problems, in a wobble signal reproducingcircuit for reproducing a wobble signal recorded by wobbling a grooveformed on a disk, the wobble signal reproducing circuit includes anarithmetic circuit for calculating a push-pull signal, a band passfilter for extracting a wobble frequency component from an output of thearithmetic circuit, an AGC (AUTOMATIC GAIN CONTROL) circuit disposed ata front stage or inside of the arithmetic circuit, and land pre-pitdetection means for detecting a land pre-pit region where a pit isformed in a land portion which is between the groove and a groove and inwhich information is not recorded, and a structure is such that a gainof the AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response timeconstant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed over bya detection signal of the land pre-pit detection means at a time ofreproduction of the land pre-pit region.

Besides, there is provided address information recording regiondetection means for detecting an address information recording regionwhere an address is formed in a portion in which the groove is dividedon a track into a land portion, and a structure is such that a gain ofthe AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response timeconstant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed over bya detection signal of the address information recording region detectionmeans at a time of reproduction of the address information recordingregion.

Further, there is provided a second AGC (AUTOMATIC GAIN CONTROL) circuitat an output of the band pass filter for extracting the wobble signalfrom the push-pull signal, and a structure is such that a gain of theAGC (AUTOMATIC GAIN CONTROL) circuit and a gain of the second AGC(AUTOMATIC GAIN CONTROL) circuit are fixed or a response time constantof the AGC (AUTOMATIC GAIN CONTROL) circuit and a response time constantof the second AGC (AUTOMATIC GAIN CONTROL) circuit are changed over at atime of reproduction of the address information recording region.

Besides, there is provided means for detecting a scratch or a fingerprint of a disk to be reproduced, and a structure is such that a gain ofthe AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response timeconstant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed by an ORoperation output of a detection signal of the means and a detectionsignal of the land pre-pit detection means.

Further, a structure is such that a gain of the AGC (AUTOMATIC GAINCONTROL) circuit and a gain of the second AGC (AUTOMATIC GAIN CONTROL)circuit are fixed or a response time constant of the AGC (AUTOMATIC GAINCONTROL) circuit and a response time constant of the second AGC(AUTOMATIC GAIN CONTROL) circuit are changed by an OR operation outputof a detection signal of means for detecting a scratch or a finger printof a disk to be reproduced and a detection signal of the addressinformation recording region detection means.

Besides, the land pre-pit detection means detects a land pre-pitrecording region by a detection signal corresponding to a land pre-pitregion position or the signal generated from the detection signal of themeans and a clock obtained in synchronization with a rotation speed ofthe disk.

Further, the address information recording region detection meansdetects an address information recording region by a detection signalcorresponding to an address information recording region position, thesignal generated from the detection signal and a wobble signal, or thesignal generated from the detection signal of the means and a clockobtained in synchronization with a rotation speed of the disk.

Besides, a pass frequency band of the band pass filter is substantiallyin proportion to a frequency of a clock obtained in synchronization witha rotation speed of the disk, and a proportionality coefficient betweenthe pass frequency band and the frequency of the clock can be changed.Further, there are provided a scratch detection circuit for detecting ascratch or a finger print of the disk, and a function for fixing thepass frequency band of the band pass filter at a time of detection ofthe scratch.

Besides, there is provided a function in which a frequency of a clockobtained in synchronization with a rotation speed of the disk ismeasured and a pass frequency band of the band pass filter is fixed whenthe frequency is largely varied at a time of normal reproduction.

Besides, an arithmetic circuit for calculating a push-pull signal has aband for permitting a land pre-pit signal of a land pre-pit region topass, and there is provided land pre-pit detection means for making theoutput of the arithmetic circuit the land pre-pit signal.

Further, a wobble signal reproducing circuit includes an arithmeticcircuit for calculating a push-pull signal, a band pass filter forextracting a wobble signal frequency component from an output of thearithmetic circuit, and a subtracting circuit for subtracting an outputof the band pass filter from the output of the arithmetic circuit, and astructure is such that the arithmetic circuit and the subtractingcircuit have bands for permitting a land pre-pit signal of a landpre-pit region to pass, and there is provided land pre-pit detectionmeans for making the output of the subtracting circuit the land pre-pitsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram of a wobble signal reproducing circuitof a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional wobble signalreproducing circuit.

FIG. 3 is a view schematically showing a land pre-pit of a DVD-R/RW.

FIG. 4 is a view schematically showing a PID region of a DVD-RAM.

FIG. 5 is a circuit block diagram showing an example of an AGC(AUTOMATIC GAIN CONTROL) circuit of the first embodiment of the presentinvention.

FIG. 6 is a schematic view showing that a land pre-pit signal leaks intoan RF signal at the time of reproduction of a DVD-R/RW.

FIG. 7 is a circuit block diagram showing an example of a band passfilter circuit of the first embodiment of the present invention.

FIG. 8 is a circuit block diagram showing an example of a band passfilter circuit of a second embodiment of the present invention.

FIG. 9 is a circuit block diagram showing an example of an AGC(AUTOMATIC GAIN CONTROL) circuit of the second embodiment of the presentinvention.

FIG. 10 is a circuit block diagram showing an example of a band passfilter circuit of the second embodiment of the present invention.

FIG. 11 is a view showing the relation between an input clock frequencyof a current source 905 of a filter of FIG. 10 and an output current.

FIG. 12 is a circuit block diagram of a wobble signal reproducingcircuit of a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to explanation of the drawings, reference numerals used in thedrawings will be explained.

1, 3 . . . optical detector, 2 . . . far field pattern, 111, 112, 1101 .. . adding circuit, 113, 114 . . . high band pass filter, 21 to 23 . . .AGC (AUTOMATIC GAIN CONTROL) circuit, 28, 117 . . . subtracting circuit,20 . . . microcomputer, 23 . . . band pass filter, 25 . . . binarizationcircuit, 26 . . . phase lock loop (PLL) circuit, 27 . . . land pre-pitdetection circuit, 301, 403, 701 . . . wobble track, 302 . . . landpre-pit, 401, 402 . . . PID portion, 502 . . . amplitude detectioncircuit, 504 . . . charge pump circuit, 601 to 603 . . . operationalamplifier, 901, 902 . . . gm variable amplifier, 905 . . . variablecurrent source, 908 . . . fixed current source, 1102 . . . scratchdetection circuit, 1104 . . . OR circuit.

FIG. 1 is a circuit block diagram of a first embodiment of the presentinvention. In the drawing, a block having the same function as a blockin FIG. 2 is designated by the same character as FIG. 2 and itsexplanation is omitted. Reference numerals 111 and 112 designate wideband adding circuits; 113 and 114, wide band HPFs; and 117, a wide bandsubtracting circuit. Reference numerals 21, 22 and 24 designate AGC(AUTOMATIC GAIN CONTROL) circuits provided with a gain hold function,and a gain is fixed by a control signal from a microcomputer 20. Amongthem, the AGC (AUTOMATIC GAIN CONTROL) circuits 21 and 22 disposed atthe front stage of a push-pull arithmetic circuit constituted by thesubtracting circuit 117 are made wide band AGC (AUTOMATIC GAIN CONTROL)circuits. However, in the case where the HPFs 113 and 114 and thesubtracting circuit 117 are defined as the push-pull arithmetic circuit,although the circuits become AGC (AUTOMATIC GAIN CONTROL) circuitsdisposed in the inside of the push-pull arithmetic circuit, thepush-pull arithmetic circuit of this embodiment indicates a subtractingportion, and hereinafter, the arrangement of the AGC (AUTOMATIC GAINCONTROL) circuits 21 and 22 is made the front stage of the push-pullarithmetic circuit. Reference numeral 27 designates a circuit fordetecting an LPP signal recorded in a DVD-R/RW, and LPP detection by thecircuit structure is made possible by making the circuits from theadding circuit to the subtracting circuit have a wide band. Referencenumeral 23 designates a BPF in which the pass band is changedsubstantially in proportion to a clock frequency, and a proportionalitycoefficient between the clock frequency and the pass band can be changedby the microcomputer 20. Reference numeral 25 designates a slice circuitwhich binarizes a wobble signal. Reference numeral 26 designates a PLLcircuit for generating a clock signal from the binarized wobble signal.Reference numerals 1101 and 1102 designate defect detection circuits fordetecting a scratch, a finger print and the like of a disk from an RFsignal. Reference numeral 101 designates a control signal to the AGC(AUTOMATIC GAIN CONTROL) circuits; and 102, a control signal to the BPF23.

FIG. 5 shows an example of a circuit structure of the AGC (AUTOMATICGAIN CONTROL) circuit 21, 22 or 23. Reference numeral 501 in the drawingdesignates a gain variable amplifier for performing gain control by avoltage V0; and 502, a detection circuit which detects an amplitude andoutputs a difference from a reference voltage VR as a control voltage.Reference numeral 504 uses the control voltage output from the wavedetection circuit 502 to perform charge and discharge of a capacitor506. Reference numeral 505 designates an AGC (AUTOMATIC GAIN CONTROL)hold switch, and when the switch is turned off, the control voltage V0of the gain variable amplifier 501 is held by the capacitor 506 and thegain of the amplifier 501 is fixed.

Hereinafter, an AGC (AUTOMATIC GAIN CONTROL) operation of thisembodiment will be described.

At the time of reproduction of a CD-R/RW, wobble is a continuous signal,and a pit does not exist in a land portion, so that leakage does notoccur. Thus, the switch 505 of FIG. 5 is always used in an on state, andthe AGC (AUTOMATIC GAIN CONTROL) operation is not held.

FIG. 6 is a schematic view showing an output waveform of an opticaldetector at the time of reproduction of a DVD-R/RW. When a signalrecorded in a wobble 701 on the disk is reproduced by a light spot 702,the amplitude of an output 703 of the optical detector of FIG. 1 isvaried as indicated by 704 by leakage of the signal by the LPP. Thus, atthe time of reproduction of the LPP, the switch 505 of FIG. 5 is turnedoff, so that the AGC (AUTOMATIC GAIN CONTROL) operation of the AGC(AUTOMATIC GAIN CONTROL) 1 and 2 at the front stage of the push-pullarithmetic circuit of FIG. 1 is held, and the gain of the AGC (AUTOMATICGAIN CONTROL) 1 and 2 does not follow the amplitude variation. Since theLPP exists in synchronization with wobbling of the groove of the disk,after the LPP detection circuit 27 of the drawing detects the first LPP,a clock signal reproduced from a wobble signal is counted by themicrocomputer to detect the LPP position, and the AGC (AUTOMATIC GAINCONTROL) operation is held. By this, AGC (AUTOMATIC GAIN CONTROL) gainvariation by the RF amplitude change at the time of reproduction of theLPP is prevented and leakage of the RF signal into the wobble signal canbe reduced. Further, in addition to the above, also with respect to theoperation of the AGC (AUTOMATIC GAIN CONTROL) 3 at the back stage of theBPF of FIG. 1, by performing the same control as the AGC (AUTOMATIC GAINCONTROL) 1 and 2, it is possible to prevent gain variation of the AGC(AUTOMATIC GAIN CONTROL) 3 by the wobble signal amplitude change at thetime of reproduction of the LPP and to stabilize the reproduction of thewobble signal.

In a DVD-RAM, as shown in FIG. 4, since data is recorded in thestaggering manner in the PID regions 401 and 402, in the case where thewobble signal is reproduced in the regions by the circuit of FIG. 1,there is a possibility that input of the AGC (AUTOMATIC GAIN CONTROL) 1and 2 becomes signalless and the operation is saturated. Besides, sincea groove does not exist in the PID region, there is a possibility thatit lacks the wobble signal at the time of reproduction in the region andthe operation of the AGC (AUTOMATIC GAIN CONTROL) 3 is saturated. Thus,at the time of reproduction in the PID region, in the AGC (AUTOMATICGAIN CONTROL) 1 to 3, the switch 505 of FIG. 5 is turned off, and theAGC (AUTOMATIC GAIN CONTROL) operation is held, so that saturation isprevented. Incidentally, since the PID region exists in synchronizationwith the wobbling of the land and the groove of the disk, after thefirst PID region is detected, a wobble signal or a clock signalreproduced from the wobble signal is counted by the microcomputer todetect the PID region, and the AGC (AUTOMATIC GAIN CONTROL) operation isheld. By this, it is possible to prevent saturation of AGC (AUTOMATICGAIN CONTROL) by lack of the wobble signal in the PID region.

By the above operation, in the circuit of FIG. 1 and FIG. 5, it ispossible to stably operate the AGC (AUTOMATIC GAIN CONTROL) circuits atthe time of recording and reproduction of the CD-R/RW, DVD-R/RW andDVD-RAM.

FIG. 7 shows an example of a circuit structure of the BPF circuit 23.Reference numerals 601, 602 and 607 designate operational amplifiers,and the operational amplifier 602, together with a switch 603 controlledby a clock signal and capacitors 604 to 606, constitutes a switchedcapacitor filter. Similarly, the operational amplifier 607, a switch 608and capacitors 609 to 611 constitute a switched capacitor filter, andthe operational amplifier 601 and the two-stage switched capacitorfilters constitute a state variable type filter. A pass band of thefilter is determined by a cut off frequency fc of the switched capacitorfilter. When a capacitance value of the capacitor 604 is C1, acapacitance value of the capacitor 606 is C2, and a switching frequencyis fsw, fc of the switched capacitor filter constituted by theoperational amplifier 602 is expressed by the following expression.fc=(1/2π)×(C1/C2)×fsw

Since fc of the filter is in proportion to the switching frequency, whenthe wobble frequency is changed by the change of reproduction speed andthe clock frequency reproduced from the wobble is changed, fc of theswitched capacitor filter is changed in proportion to that. By this, thepass band of the BPF can be made substantially proportional to thewobble frequency, and band setting of the BPF by means such as registersetting of the microcomputer from the outside becomes unnecessary, sothat troublesome processing can be reduced. Further, it is possible toreduce a drop in SIN of the wobble signal by a deviation between bandsetting of the BPF and the wobble signal frequency, and to reduce anincrease in jitter of clock generated from the wobble signal.

The ratio of the wobble frequency to the clock frequency in the DVD-R/RWand DVD-RAM is 1:186, which is different from the ratio 1:196 of thewobble frequency to the clock frequency in the CD-R/RW. This differenceis treated in such a manner that switches 612 and 613 are changed overby a control signal 102 of FIG. 7 to change the capacitance value C1, sothat a proportionality coefficient between fc and fsx is changed.According to this structure, by the BPF of FIG. 1 and FIG. 7, it ispossible to deal with high speed recording, high speed reproduction,variable recording such as CAV, and variable reproduction of CD-R/RW,DVD-R/RW, and DVD-RAM.

Incidentally, in the case where the wobble signal is not reproduced by ascratch, a finger print and the like of a disk, since the clock comesnot to be reproduced, the pass band of the filter becomes unstable.Thus, a defect signal obtained by the defect detection circuit is made aBPF hold signal 617 to control switches 615 and 616, and the switchesare connected to the resister side at the time of detection of thedefect, so that the band of the filter is fixed.

Like this, according to the circuit structure of the first embodiment,one wobble signal reproducing circuit can deal with high speedrecording, high speed reproduction, variable recording such as CAV, andvariable reproduction of CD-R/RW, DVD-R/RW, and DVD-RAM to reproduce thestable wobble signal, and the circuit mounting area in the optical diskreproducing device can be greatly reduced.

Next, a second embodiment of the present invention will be described.FIG. 8 is a block diagram of this embodiment. In the drawing, a blockhaving the same function as a block of FIG. 1 is designated by the samecharacter as FIG. 1 and the explanation is omitted. Reference numeral 28designates a wide band subtracting circuit, which subtracts an output ofa BPF 23 from a wide band push-pull output obtained by a subtractingcircuit 117. By this, a wobble frequency component can be removed fromthe LPP output of FIG. 1, and more stable LPP detection becomespossible.

FIG. 9 shows an example of a structure of an AGC (AUTOMATIC GAINCONTROL) circuit in this embodiment. In the drawing, a block having thesame function as the AGC (AUTOMATIC GAIN CONTROL) circuit of FIG. 5 isdesignated by the same character, and the explanation is omitted.Reference numeral 801 designates a capacitor change-over switch, whichchanges over capacitors 506 and 802 by a control signal 101. Capacitancevalues CO and C1 in the drawing are made to have the following relation.C1>>C0

An AGC (AUTOMATIC GAIN CONTROL) operation of this embodiment will behereinafter described.

At the time of reproduction of a CD-R/RW, since an RF signal and awobble signal are stably reproduced without leakage, intermittence, orthe like, the switch 801 selects the capacitor 506 having the smallcapacitance value and does not perform change-over.

At the time of reproduction of a DVD-R/RW, as shown in FIG. 6, sincethere is an amplitude variation due to leakage of an LPP into an RFsignal, the switch 801 is changed over to select the capacitor 802having the large capacitance value at the time of reproduction of theLPP. By this, the response time constant of the AGC (AUTOMATIC GAINCONTROL) becomes large, and response becomes slow. Thus, the AGC(AUTOMATIC GAIN CONTROL) comes not to follow the RF amplitude variationand the wobble amplitude variation due to the leakage of the LPP, andsimilarly to the embodiment 1, the effect of stabilizing the wobbleamplitude can be obtained. The detection of the LPP is performed,similarly to the embodiment 1, by counting the clock signal reproducedfrom the wobble signal by the microcomputer.

At the time of reproduction of a DVD-RAM, since AGC (AUTOMATIC GAINCONTROL) input becomes signalless in the PID region, the switch 801 ischanged over at the time of reproduction of the PID region, and theresponse time constant of the AGC (AUTOMATIC GAIN CONTROL) circuit ismade large. Similarly to the embodiment 1, the detection of the PIDregion is performed by counting the clock signal reproduced from thewobble signal by the microcomputer. By this, an erroneous operation ofthe AGC (AUTOMATIC GAIN CONTROL) by input without signal is prevented,and it is possible to stably operate the AGC (AUTOMATIC GAIN CONTROL)even at the time of passing through the PID region.

From the above, also in this embodiment, similarly to the embodiment 1,the AGC (AUTOMATIC GAIN CONTROL) can be stably operated at the time ofrecording and reproduction of the CD-R/RW, DVD-R/RW and DVD-RAM, and thesame effect as the embodiment 1 can be obtained.

FIG. 10 shows an example of a structure of the BPF circuit in thisembodiment. Reference numerals 901 and 902 designate gm variableamplifiers, and gm (mutual conductance of output current to inputvoltage) is changed substantially in proportion to the value of currentfrom a current source 905. This circuit constitutes a biquartic filterby the amplifiers 901 and 902 and capacitors 903 and 904. By making acurrent source 905 for controlling gm have such a structure that anoutput current value is substantially in proportion to an input clockfrequency, similarly to the BPF circuit of the embodiment 1, the passband of the BPF can be changed substantially in proportion to the changeof the reproduction speed.

Further, by a control signal 102, as shown in FIG. 11, by changing theproportionality coefficient between a clock frequency and an outputcurrent in the current source 905, it is possible to deal with diskshaving different ratios of the wobble frequency to the clock frequency,such as CD-R/RW, DVD-R/RW, and DVD-RAM, and the same effect as the BPFcircuit of the embodiment 1 can be obtained. Incidentally, a defectsignal obtained by a defect detection circuit is made a hold signal 617to control a switch 907, and the switch 907 is connected to a fixedcurrent source at the time of detection of a defect. By this, in thecase where it lacks the wobble signal by a scratch, a finger print orthe like of the disk and the clock is not reproduced, the pass band ofthe BPF can be fixed, and the filter can be stably operated.

By the structure of the AGC (AUTOMATIC GAIN CONTROL) circuit and the BPFcircuit, even in the embodiment 2, the same effect as the embodiment 1can be obtained.

FIG. 12 is a circuit block diagram of a third embodiment of the presentinvention. In the drawing, a block having the same function as a blockof FIG. 1 is designated by the same character as FIG. 1, and theexplanation is omitted. Reference numeral 101 in the drawing designatesa control signal for holding the operation of the AGC (AUTOMATIC GAINCONTROL) circuit or for changing the response time constant in theembodiments 1 and 2, and the control signal and a defect detectionsignal 618 of a scratch, a finger print or the like outputted from adefect detection circuit 1102 are inputted to an OR circuit 1104 togenerate an AGC (AUTOMATIC GAIN CONTROL) control signal 1105. By this,with respect to not only the LPP region of the DVD-R/RW and the PIDregion of the DVD-RAM but also the defect such as a scratch of the disk,the AGC (AUTOMATIC GAIN CONTROL) operation can be made stable, and thereliability of the wobble signal can be improved.

Besides, the frequency of the clock signal reproduced from the wobblesignal is monitored by a microcomputer, and in the case where a largevariation occurs in the frequency at the time of normal reproduction,the BPF hold signal 617 is outputted. By this, in the case where thewobble signal is not reproduced by a scratch, a finger print or thelike, and the clock signal is not reproduced, the pass band of the BPFcan be fixed, and the filter can be stably operated.

As described above, in this embodiment, the push-pull signal detectioncircuit is made to have a wide band, and the push-pull signal output isinputted to the LPP detection circuit at the time of reproduction of theDVD-R/RW to detect the LPP. By this, the LPP signal can be detected bythe wobble signal reproducing circuit and the circuit scale can bereduced.

Besides, there is provided a function in which the operation of the AGC(AUTOMATIC GAIN CONTROL) circuit for removing the RF signal withprecision and the AGC (AUTOMATIC GAIN CONTROL) circuit at the back stageof the BPF circuit can be held by the control signal from themicrocomputer, or the time constant can be changed over. By this, it ispossible to suppress variation of the AGC (AUTOMATIC GAIN CONTROL) byleakage of the LPP signal into the RF signal in the LPP region at thetime of reproduction of the DVD-R/RW. Besides, it is possible to preventan erroneous operation such as saturation of the AGC (AUTOMATIC GAINCONTROL) output by disappearance of the wobble signal in the ID regionat the time of reproduction of the DVD-RAM.

Further, such structure is adopted that the pass band of the BPF forextracting the wobble frequency is substantially in proportion to theclock frequency reproduced from the wobble, and the proportionalitycoefficient between the clock frequency and the pass band of the BPF canbe changed over. By this, with respect to the disks having differentratios of the wobble frequency to the clock frequency, such as theCD-R/RW, DVD-R/RW and DVD-RAM, the wobble frequency can be extractedusing the same BPF.

Incidentally, the circuit structures illustrated in the embodiment 1 tothe embodiment 3 of the present invention are merely examples, and theAGC (AUTOMATIC GAIN CONTROL) circuit and the BPF circuit are not limitedto the embodiments of the present invention. Besides, the combination ofthe structure of the LPP detection circuit, the method of holding theAGC (AUTOMATIC GAIN CONTROL) circuit and changing over the timeconstant, and the method of fixing the pass band of the BPF is not alsolimited to the embodiments of the present invention.

As described above, with respect to the recordable and reproducibleoptical disk such as the CD-R/RW, DVD-R/RW and DVD-RAM, one wobblesignal reproducing circuit can stably reproduce the wobble signal, andfurther, by this circuit, LPP detection in the DVD-R/RW can also beperformed. By this, a circuit mounting area in the optical diskreproducing device can be greatly reduced.

1. A wobble signal reproducing circuit for reproducing a wobble signalrecorded by wobbling a groove formed on a disk, comprising: anarithmetic circuit for calculating a push-pull signal; a band passfilter for extracting a wobble frequency component from an output of thearithmetic circuit; an AGC (AUTOMATIC GAIN CONTROL) circuit disposed ata front stage or inside of the arithmetic circuit; and land pre-pitdetection means for detecting a land pre-pit region where a pit isformed in a land portion which is between the groove and a groove and inwhich information is not recorded, wherein a gain of the AGC (AUTOMATICGAIN CONTROL) circuit is fixed or a response time constant of the AGC(AUTOMATIC GAIN CONTROL) circuit is changed over by a detection signalof the land pre-pit detection means at a time of reproduction of theland pre-pit region. 2-3. (canceled)
 4. A wobble signal reproducingcircuit according to claim 1, further comprising means for detecting ascratch or a finger print of the disk to be reproduced, wherein a gainof the AGC (AUTOMATIC GAIN CONTROL) circuit is fixed or a response timeconstant of the AGC (AUTOMATIC GAIN CONTROL) circuit is changed by an ORoperation output of a detection signal of the means and a detectionsignal of the land pre-pit detection means.
 5. (canceled)
 6. A wobblesignal reproducing circuit according to claim 1, wherein the landpre-pit detection means detects a land pre-pit recording region by adetection signal corresponding to a land pre-pit region position or thesignal generated from the detection signal of the means and a clockobtained in synchronization with a rotation speed of the disk. 7-12.(canceled)